Photocurable organopolysiloxane compositions

Abstract

A novel photocurable organopolysiloxane composition is proposed capable of giving a cured product having a very high anti-moisture resistance even at an elevated temperature to withstand a treatment in boiling water for 1 hour or longer without coming off from the substrate surface on which it has been applied and cured by irradiation with light. The composition comprises a specific acryloyloxy-containing organopolysiloxane as the base component, an epoxy compound and a photosensitizer. The composition is suitable, for example, for providing a moisture-proof overcoating on various electronic parts such as a capacitor.

What is claimed is: 
     
       1. A photocurable organopolysiloxane composition which comprises (a) 100 parts by weight of an acryloyloxy-containing organopolysiloxane represented by the average unit formula ##STR8##   where R 1  is a divalent hydrocarbon group, R 2  is a monovalent hydrocarbon group, at least one of the groups denoted by X is an acryloyloxy-substituted 2-hydroxyalkyl group represented by the general formula ##STR9##   in which R 3  is a hydrogen atom or an alkyl group having from 1 to 4 carbon atoms and R 4  is a divalent hydrocarbon group, the remainder of the groups denoted by X each being a hydrogen atom, n is zero or a positive integer not exceeding 4, a is a positive number not exceeding 3 and b is zero or a positive number smaller than 3 with the proviso that a+b is a positive number not exceeding 3,   (b) from 0.1 to 20 parts by weight of an epoxy-containing compound having at least one epoxy group in a molecule, and   (c) a photosensitizer.   
     
     
       2. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the divalent hydrocarbon group denoted by the symbol R 1  is an alkylene group selected from the class consisting of methylene, ethylene and propylene groups. 
     
     
       3. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the divalent hydrocarbon group denoted by the symbol R 4  is an alkylene group selected from the class consisting of methylene, ethylene and propylene groups. 
     
     
       4. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the divalent hydrocarbon group denoted by the symbol R 1  is a propylene group. 
     
     
       5. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the group denoted by the symbol X other than hydrogen atoms is a group expressed by the structural formula ##STR10## 
     
     
       6. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the epoxy-containing compound is selected from the class consisting of allyl glycidyl ether, butyl glycidyl ether, glycidyl methacrylate, 3,4-epoxy-6-methylcyclohexyl-3,4-epoxy-6-methylcyclohexane carboxylate, vinylcyclohexane dioxide, dipentene dioxide, dicyclopentadiene dioxide, bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, diglycidyl phthalate, phenol-novolac epoxy resins, triglycidyl isocyanurate and bisphenol A-type epoxy resins. 
     
     
       7. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the epoxy-containing compound is an epoxy-containing organosilane represented by the general formula   R.sub.c.sup.5 SiZ.sub.4-c,     wherein R 5  is a substituted or unsubstituted monovalent hydrocarbon group, Z is a hydroxy group or a hydrolyzable atom or group and c is an integer of 1, 2 or 3, at least one of the groups denoted by R 5  being a substituted monovalent hydrocarbon group having a substituent with an epoxy group.   
     
     
       8. The photocurable organopolysiloxane composition as claimed in claim 7 wherein the epoxy-containing organosilane is selected from the class consisting of 3-glycidoxypropyl trimethoxysilane, 2-(3,4-epoxycyclohexyl) ethyl trimethoxysilane and partial hydrolysis-condensation products thereof having a degree of polymerization not exceeding about 10. 
     
     
       9. The photocurable organopolysiloxane composition as claimed in claim 1 wherein the amount of the photosensitizer is in the range from 0.01 to 30 parts by weight per 100 parts by weight of the component (a). 
     
     
       10. The photocurable organopolysiloxane composition as claimed in claim 1 further comprising a viscosity-improver which is a vinylic or an acrylic monomer polymerizable by addition polymerization and having a boiling point not lower than 100° C. under atmospheric pressure. 
     
     
       11. The photocurable organopolysiloxane composition as claimed in claim 10 wherein the amount of the viscosity-improver is not exceeding 500 parts by weight per 100 parts by weight of the component (a).